Alkalinity sources are used in laundry detergent compositions for a variety of reasons, one of which is to provide detersive action and improved soil removal performance. Typical sources of alkalinity include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, and alkaline earth metal silicates including potassium silicate and sodium silicate.
The performance of any detergent is affected by the hardness of the wash water, with higher levels of hardness, or calcium ion content, typically reducing the detergency or soil removal performance of the detergent. Alkaline detergents, particularly those intended for institutional and commercial use, generally contain phosphates, nitrilotriacetic acid (NTA) and ethylenediaminetriacetic acid (EDTA) to remove soils and to sequester metal ions such as calcium, magnesium, and iron.
In particular, phosphates, NTA or EDTA are used in detergents because of their ability to solubilize pre-existing inorganic salts and/or soils. When calcium, magnesium and iron salts precipitate, the crystals may attached to the surface being cleaned and cause undesirable effects. In the laundering area, if calcium carbonate precipitates and attaches onto the surface of fabric, the crystals may leave the fabric feeling hard and rough to the touch. In addition to encrustation, high levels of water hardness also contribute to graying of the fabric.